Antoni Lombarte

Otolith size changes related with body growth, habitat depth and temperature

SynopsisSize variation in the sagittal otoliths of six species of the genus Merluccius, and five species of the genus Coelorhynchus was compared, using a digital image processing system and multivariate analysis. It is proposed that otolith growth occurs under dual regulation, overall shape is regulated genetically, and otolith size is influenced by environmental conditions. The decline of temperature with increasing habitat depth seems to be an important factor regulating the growth of otoliths in carbonate-saturated levels. The relative growth of the otoliths is usually negatively allometric.

Otolith shape contour analysis using affine transformation invariant wavelet transforms and curvature scale space representation

Fish otolith morphology has been closely related to landmark selection in order to establish the most discriminating points that can help to differentiate or find common characteristics in sets of otolith images. Fourier analysis has traditionally been used to represent otolith images, since it can reconstruct a version of the contour that is close to the original by choosing a reduced set of harmonic terms. However, it is difficult to locate the contours singularities from this spectrum. As an alternative, wavelet transform and curvature scale space representation allow us to quantify the irregularities of the contour and determine its precise position. These properties make these techniques suitable for pattern recognition purposes, ageing, stock determination and species identification studies. In the present study both techniques are applied and used in an otolith classification system that shows robustness against affine image transformations, shears and the presence of noise. The results are interpreted and discussed in relation to traditional morphology studies.

Sagittal otolith size and shape variability to identify geographical intraspecific differences in three species of the genus Merluccius

A study was carried out on the morphology (size and shape) of the saccular otolith (sagitta) by means of image analysis on three species of the genus Merluccius (M. gayi, M. hubbsi and M. merluccius). By digitization of the sagittae, morphometry and outline (Fourier harmonic) as form descriptor measurements were obtained, that were subsequently analysed by means of multivariant methods, allowing the intraspecific variability to be quantified. The differences in the intraspecific sagittal otolith variability confirmed spatial differences of predicted groups. The results were associated with environmental and population aspects. The use of combined morphometric measurements for the whole otolith and its corresponding sulcus acusticus were very appropriate for determining the origin of the analysed otoliths. Using both principal components analysis and discriminant analyses, a clear geographical differentiation was obtained for Merluccius gayi (from Chile and Peru) and M. merluccius (from the Atlantic and Mediterranean). In both species, the discriminant analysis predicted that all the sagittae could be correctly assigned within each of the groups studied. However, it was a little less effective at differentiating between the two groups of M. hubbsi (from the San Matias Gulf on the Patagonian Shelf and Argentinian-Uruguayan Common Fishing Zone). As a result, the morphometric analysis of the sagittae otoliths acted as a clear diagnostic tool to differentiate individuals from different geographical distribution areas.

Changes in otolith area: sensory area ratio with body size and depth

SynopsisThe ratio between the sensory areas of the sulcus acusticus and the sagittal otolith (S : O ratio) in the species Merluccius capensis and M. paradoxus was analyzed using a digital image processing system. Sagittal growth in both species is negatively allometric with respect to total fish length but is more negative in the deeper-dwelling species, Merluccius paradoxus. In contrast, the sulcus acusticus undergoes a relative increase in size, that is, the S : O ratio increases with fish length. There was a clear relationship between the increase in the S : 0 ratio and depth.

Ecomorphological trends and phylogenetic inertia of otolith sagittae in Nototheniidae

A quantitative ecomorphological study was carried out on the sagitta otoliths of Antarctic and Subantarctic nototheniids, a particularly interesting family due to its fast adaptive radiation into different life strategies. We analyzed the otolith shape and size of 18 nototheniids to test the relationship between phylogeny, otolith characters and trophic niche. Relative size (area, length, width, perimeter and weight) and shape (biometric warp analysis based on homologous and pseudo-homologous landmarks) measurements were compared with phylogenic, habitat dwelling and food composition analyses. The results of the multivariate analysis of these factors indicate that there is a weak relationship between otolith shape of nototheniids and phylogeny; however, there is a clear correspondence between relative otolith size and shape and their trophic niche. The most benthic feeders of the family had the largest sagittae in relation to body size, and pelagic species had smaller and rounder shaped sagittae than benthic species. Consequently, in ecomorphological studies, it is useful to analyze the size and shape of sagittae. The discoidal shape of pelagic species, such as Pleuragrama antracticum, can be considered as a paedomorphic characteristic, converging to the juvenile sagittae of many species, which exhibit round sagittae that become elongated as they grow.

Variability of the sulcus acusticus in the sagittal otolith of the genus Merluccius (Merlucciidae)

Abstract The morphology of the sulcus acusticus of the sacular otolith (sagitta) was studied by means of image analysis on 12 extant species of the genus Merluccius . The digitization of the sulcus acusticus and the subsequent biometric analysis, by means of multivariate methods and the Fourier descriptors of the perimeters obtained, allowed the interspecific variability to be quantified. These results were in agreement with ecomorphologic (functional and environmental) and phylogenetic aspects. Analysis of the perimeters of the sulcus acusticus demonstrated a specific character and indicated the existence of two large groups: the American species and the Euro-African species, matching the phylogenetic lines. The principal difference between the two groups was found in the development of the caudal colliculum, which was relatively shorter in the American species. Within the Euro-African group, the deep-water species M. polli and M. paradoxus showed different characteristics with respect to the species from surface waters. Given the sensorial nature of the associated acoustic macula of the inner ear the sulcus is more likely to accurately reflect the species specific changes in otolith morphology.

Influence of Benguela upwelling on the structure of demersal fish populations off Namibia

The effect of bottom-water dissolved oxygen on the structure of demersal fish communities off south Namibia was analized. Collections were made during two cruises of the zone in winter 1987 and summer 1988, i.e., before and after the intensive upwelling season. Multivariate analysis revealed four distinct associations, separated by latitude (ca 27°S) and depth (ca 300 m isobath), indicating that dissolved oxygen is an important factor affecting the distribution of demersal fish communities in the zone. Faunal diversity decreased in areas of low oxygen levels. The seasonal variation in upwelling reflected the extent of fish association, their composition, and the seasonal geographical displacement of their boundaries.

Ecomorphological trends in the Artedidraconidae (Pisces: Perciformes: Notothenioidei) of the Weddell Sea

An ecomorphological study was performed on ten species of the family Artedidraconidae, the most benthic of the suborder Notothenioidei. These species are sympatric on the shelf of the Weddell Sea. The results show that the four genera comprising the family (Artedidraco, Dolloidraco, Histiodraco and Pogonophryne) can be differentiated by just a few morphometric features of their sensory organs and mouth. The genera were also clearly defined by the composition of their diet (benthic and epibenthic), the size of their prey, and their bathymetric distribution. Comparison of the morphological and ecological data shows a very close connection between sensory organs development, the mouth and bathymetric distribution. The morphological and ecological divergence observed can be explained as the result of the rapid adaptive radiation of the artedidraconids. The results confirm that characteristics of the sensory organs and alimentary structures are very suitable for the ecomorphological study of fishes.

Otolith shape feature extraction oriented to automatic classification with open distributed data

The present study reviewed some of the critical pre-processing steps required for otolith shape char- acterisation for automatic classification with heterogeneous distributed data. A common procedure for optimising automatic classification is to apply data pre-processing in order to reduce the dimension of vector inputs. One of the key aspects of these pre-processing methods is the type of codification method used for describing the otolith contour. Two types of codification methods (Cartesian and Polar) were evaluated, and the limitations (loss of infor- mation) and the benefits (invariance to affine transformations) associated with each method were pointed out. The comparative study was developed using four types of shape descriptors (morphological, statistical, spectral and multiscale), and focused on data codification techniques and their effects on extracting shape features for automatic classification. A new method derived from the Karhunen-Loeve transformation was proposed as the main procedure for standardising the codification of the otolith contours.

Statolith identification of Mediterranean Octopodidae, Sepiidae, Loliginidae, Ommastrephidae and Enoploteuthidae based on warp analyses

The statoliths of 14 species (193 right statoliths from subadult to adult individuals), belonging to five Cephalopoda families (Sepiidae, Loliginidae, Enoploteuthidae, Ommastrephidae and Octopodidae) were analysed using morphometric methods based on landmarks (geometric morphometry). The aim of the current study is to determine the discriminating power of statolith shape analysis in species identification of Mediterranean cephalopods. Discriminant analyses of the partial warps were able to fully identify (100% discrimination) the species of all families, except Octopodidae which showed some misclassification (correctly classified about 68-90%). These results were also shown by relative warp analysis. Octopodidae statoliths were studied for the first time using geometric landmark-based methods. Greatest differences in statolith shape between Octopodidae species, were in the area that unites the statolith dome with the flat wing. Landmark analysis applied to statoliths can be a useful taxonomic tool in the identification of closely related species.